1. Field of the Invention
This invention is directed to a method and apparatus for providing full duplex communication on existing simplex ring communication networks.
2. Description of Prior Art
Ring communication networks in computing systems, and particularly twisted-pair wire communication networks, have been one-way ring communication systems with computer work stations acting as communication relay stations around the ring. FIG. 1 shows a typical simplex communication system using twisted-pair wire between each workstation in a ring. By way of example, three workstations 10, 12 and 14 are shown connected to Token Ring network through IBM 8228 terminal boxes 16, 18 and 20 (also known as Padre boxes). The twisted-pair wire links 22, 24 and 26 between Padre boxes 16, 18 and 20 complete the ring.
Simplex communication around the ring moves counter-clockwise; i.e., workstation 10 to workstation 12 to workstation 14 and back to workstation 10. At terminal box 16, the signal is received at a first set of coils 28 where the signal is inductively coupled to a twisted-pair wire link 30 to workstation 10. Transceiver 32 (for example, a Token Ring adapter card) receives the signals over link 30 and reads the destination address in the message. If the message is to be delivered to workstation 10, it is passed to the workstation's processor. If the message is not addressed to workstation 10, transceiver 32 retransmits the signal out on twisted-pair wire link 34 at full power to a second set of coils 36 in terminal box 16. The signal is inductively coupled across coils 36 to link 22 for passage to terminal box 18 and workstation 12. In this manner, the communication signal from any one workstation will travel around the ring to reach any other workstation on the ring to which the signal is addressed.
There are a very large number of simplex ring communication networks, such as the example in FIG. 1 currently installed in data processing offices. It would be a significant enhancement to all of these installed systems if the systems could be converted to full duplex communication operations without rewiring the communication links and the terminal boxes. In such a duplex ring, communication signals would independently counter-rotate around the single ring between workstations.
Double-ring communication systems, with each station connected to both rings and signals rotating in one direction on each ring and in opposite directions on the two rings, are well known. Exemplary of such systems are the networks and stations taught in U.S. Pat. No. 4,663,748, entitled "Local Area Network," U.S. Pat. No. 4,752,924, entitled "Ring Packet Switch," and U.S. Pat. No. 5,049,871, entitled "Loop Communication System." None of these patents teach a single ring with duplex communication.
Another technique for increasing the signal carrying capacity on a twisted-pair wire ring is to use frequency couplers, or filters, in the ring to separate signals at different frequencies. An example of such a communication system is described in U.S. Pat. No. 4,885,747, entitled "Broadband and Baseband LAN." This does increase the throughput of the ring, but communications on the ring are still simplex.